Method for straightening oil-well casings or the like



W. M. FRAME Oct. 31, 1939.

METHOD FOR STRAIGHTENING OIL-WELL CASINGS OR THE LIKE Filed July 29,1957 4 Sheets-Sheet l INVENIOR.

BY @nmfb uewwv 4 M A 0 ATTORNEYS.

W i TNESSES Oct. 31, 1939. w F M v 2,178,141

METHOD FOR STRAIGHTENING OIL-WELL CASINGS OR THE LIKE Filed July 29,1957 4 Sheets-Sheet 2 k; ATTORNEYS.

Oct. 31, 1939. w, M 2,178,141

METHOD FOR STRAIGHTENING OIL-WELL CASING S OR THE LIKE Filed July 29,1937 4 Sheets-Sheet 3 W I TNESSES: INVENTOR- LLG ATTORNEYS.

Patented Oct. 31 1939 UNITED STATES PATENT OFFICE METHOD FORSTRAIGHTENING OIL-WELL CASINGS OR THE LIKE Application July 29, 1937,Serial No. 156,289

11 Claims. (Cl. 29-156) The invention relates to methods of cold- 10used prior to my invention, well casing has certain characteristics thatmaterially lessen its resistance to collapse, which is quite undesirablebecause one of the prime requisites of casing for the deep wells thatare now being drilled is that 1') it possess a satisfactory highresistance to collapse.

Well casing has been cold-straightened largely, if not entirely, by oneor the other of two forms of straightening apparatus, one a cross-roll20 straightener used extensively, if not exclusively, for thestraightening of seamless well casing, and the other a die-pressingstraightener used to some extent for the cold-straightening ofelectrically welded casing.

25 In the operation of a cross-roll straightener, casing is rotatedabout its axis and fed forwardly by pairs of cross-rolls, and isconcurrently and progressively deflected transversely of its, axis by apressure roll or rolls positioned between the 30 pairs of cross-rolls. Ihave found that this action of cross-roll straighteners results in theformation of residual compression stresses in the inner and residualtension stresses in the outer wall fibers of well casing. That suchpeculiar 35 residual stresses diminish the resistance of casing tocollapse appears from a consideration of the stresses to which casing issubjected when under external fluid pressure in awell. It'is known thatwhen a hollow. cylinder is subjected to external fluid pressure-thecompressive stress is greater in the inner than in the outer fibers ofthe wall. casing are under residual compressive stresses, as are thoseof easing which has passed through a cross-roll straightener, and whenthe casing is subjected to externally applied fluid pressure such asencountered in a well, the compressive stress due to the applied had isadded to the residual inner compressive stress with the result 50 thatcollapse of the casing occurs at a lower applied load than if noresidual stress were present in a casing which was otherwise the same.

Aside from these residual stresses being unfavorable and prejudicial forthe reasons just ex- 55 plai'ned, they are objectionable because theyare Also, when the inside fibers of well frequently not uniform aroundthe circumference of easing. Due to variations in the structure ofcommercial steel, variations in wall thickness and other dimensions ofeasing arising from manufacturing methods, and also to other causes, 5the residual tension or compression, or both, may so varycircumferentially of casing, and with relation to each other, that theydistort the casing from its desiredcylindrical form when subjected tocross-roll straightening. By reason of such distortion, as well as byreason of its unfavorable residual stresses, the resistance to collapseof casing which has passed through a crossroll straightener ismaterially lowered. 4

Die-pressing straighteners, mentioned above, comprise two cooperatingdies, each provided with a casing-engaging cylindrical groove of about180 degrees, and mounted for relative lateral reciprocation to and froma casing to plastically compress it, the casing being fed longitudinallyinto these dies without rotating it on its axis between pressingoperations. By testing casing that has been so die pressed, I have foundthat the metal was not uniformly cold worked throughout thecircumference of the casing. The cold working was greatest in theportions of the casings that were at and adjacent to the lines ofjoinder of the two-part dies, and at least in the portions of the casingthat were at and adjacent to the medial portions or valleys of the dies.For 80 example, impact tests on specimens out from the first-mentionedportions of such casing, namely, those that were at the lines of joinderof the dies when the casing was compressed, showed impact resistancesmaterially below those of specimens cut from the second-mentionedportions of the casing, which is another way of stating that theportions of the casing at and adjacent to the lines of joinder of thedies had less ductility than the portions at and adjacent to the valleysof the dies;

While this variation in ductility is objectionable in itself,particularly when the portions of the casing at and adjacent to thelines of joinder of the dies is so brittle that the casing may breakunder service conditions, the residual stresses in the casing arisingfrom the non-uniform plastic flow of its metal are particularlyobjectionable because they ultimately result in a distortion of thecasing to such out-of-roundness as to mate- 5o rially lessen itsresistance to collapse. In such a die-pressed casing its inner wallfibers are under residual tension and its outer wall fibers underresidual compression stresses, but the residual tension and compressionstresses in the portions of the casing that were at and adjacent to thelines of joinder of the dies are materially greater than those in theother portions of the casing, namely, those that were at and adjacent tothe valleys of the dies. The result of this is that when the casing isfreed from the dies the unequal residual stresses so distort the casingthat it is of a general elliptical shape, its major axis being in thedirection of the casing that extended from one to the other of theportions of it that were at the lines of joinder of the dies. It is wellunderstood that out-of-roundness of a tubular body materially diminishesits resistance to collapse.

5 In addition to the foregoing objectionable characteristics of wellcasing that has been subjected to cross-roll straighteners, it is wellknown that in the operation of cross-roll straighteners there can be nostraightening of the end portions of cylindrical articles that arepassed through them. This results in a material endcropping loss of wellcasing that has been passed through cross-roll straighteners. Also, Ihave found that casing which has been subjected to die-pressingstraighteners of the type explained lacks longitudinal straightness toan objectionable extent.

Objects of my invention are to provide a method of and apparatus for sostraightening well casing that it is substantially free from suchunfavorable and objectionable residual stresses that its resistance tocollapse is lessened, and that it is axially straight and of suchroundness that it is highly resistant to collapse, and to providecold-straightened casing that is round,

straight and highly resistant to collapse.

In the practice of my invention well casing, of the seamless, welded, orany other type, is coldstraightened by reducing it in diameter in such away that the plastic flow of its metal may result in imparting to themetal residual stresses that increase the resistance of the casing tocollapse, and in all events avoid imparting objectionable residualstresses thereto. This reduction in diameter is effected by subjectingthe casing, increment after increment and progressively from end to end,to repeated radial pressure applied solely to the exterior of the casingand substantially uniformly about its circumference. The pressure ispreferably applied to the casing by a die formed of not less than threecomplemental members mounted for repeated lateral reciprocation to andfrom closed position. The uniformity of the application of pressure to acasing may be effected by increasing the number of complemental membersforming the die, but is preferably effected by repeated compressions ofsmall increment of the casing accompanied by turning the casing on itsaxis between repeated applications of pressure. So that the pressurewill be applied solely to its exterior, the interior of the casing isnot provided with a mandrel or any other pressure-applying orwall-supporting instrumentality or medium. 5 This repeateddiameter-reducing pressure causes the metal of the casing to flowplastically in a substantially uniform manner around the casing.

While thus subjected to this plastic flow, the successive increments ofthe casing are molded to uniform-diameter cylindrical form, each inaxial alignment with increments that have been previously molded to suchform. This molding is effected by the shaping of the interiorcasingengaging portions of the complementai die members. Preferably,each untreated increme the casing is first molded to tapered form, andthis is preferably done in a plurality of pressureapplying steps betweeneach of which the casin is turned on its axis an angular amount equal toone-half of the arcuate extent of each complemental die member, but itmay be turned more or less than this amount. Immediately following thetapering of each increment, it is further compressed to plastically moldit to cylindrical form, preferably in a portion of the die immediatelyadjoining its taper-forming section, and when each increment is thusreduced to cylindrical form, it is advanced in the cylindrical portionof the die where it is elastically compressed in the nextpressure-applying operation. The effect of this is to axially align witheach elastically compressed increment the succeeding tapered incrementthat is being plastically reduced to a cylindrical form of the samediameter, which action proceeds progressively from end to end of thecasing.

As a result of this manner of straightening well casing, I have foundthat it is axially straight and circumferentially round within thecommercial contemplation of these terms. It is straighter and more trulycylindrical than well casing that has been cold-straightened on anycommercial straightener known to me. In addition to this, I have foundthat the metal of casing may have, throughout, substantially uniformresidual tension stresses in its inner and substantially uniformresidual compression stresses in its outer fibers. These residualstresses increase the resistance of the casing to collapse, as comparedto casing not so stressed and otherwise the same. When the casing issubjected in service to external fluid pressure, the compressive forcesso imparted to it must first relieve the residual tension stresses inthe inner wall fibers of the casing before such fibers become subjectedto the compressive collapse-producing stresses produced by the appliedfluid-pressure load, which manifestly results, as stated, in increasingthe resistance of the casing to collapse. In addiiton to this favorableaction of the residual stresses, their uniformity c-ircumferentially ofthe casing maintains the casing in its cylindrical straightened form.Hence, well casing that is cold-straightened according to my inventionhas, by reason of its shape and the residual stresses of its metal,collapse-resistingcharacteristics materially superior to priorcoldstraightening well casing.

My invention will be further explained with reference to theaccompanying drawings, of which Fig. 1 is a side elevation of apparatuswhich may be used in the practice of the invention; Fig. 2 a plan viewof the apparatus shown in Fig. 1; Fig. 3 a longitudinal centralsectional View of the preferred form of a die member used in theapparatus of Figs. 1 and 2; Figs. 4 to 10 diagrammatic views of the diemember of Fig. 3 illustrating the progressive incrementaldiameter-reducing action of the die; and Fig. 11 a transverse sectionalview of the die member taken on the line Fig. ii but illustrating thethree complemental members forming the complete die.

Referring to Figs. 1 and 2, a casing is shown as being passed through apress i having complemental die members, usually three in number andhereinafter described in detail, which are closed around the casing tostraighten it. The die members are reciproc'ated radially of the casing,usually the rotation of eccentrics which may be driven in any suitablemanner, as by shafts 2. Except for the structure of the die and thegeneral construction and operation of the apparatus in which it is used,the apparatus forms no part of my invention. A preferred form ofdie-actuating apparatus is that shown in patent application Serial No.140,635,

filed May 4, 1937, by F. C. Biggert, Jr.

Briefly describing the apparatus, the casing may be supported on eachside of the press by mechanisms 3 and 4 which feed the casing forwardlyincrement by increment between the pressure-applying, diameter-reducingmovements of the die members and also for concurrently turning thecasing on its axis. Specifically, each of the mechanisms may include achuck III for releasably gripping the casing during the forward feedingmovement only which chuck is rotatably received in a carriage llslidably mounted on a 20 base I2. To obtain the incremental forwardfeeding movement of the casing each carriage II .is moved forward andback on its base l2 by suitable means which may comprise a crank andconnecting rod drive l3, each of which is con- 25 nected by shafts I4 toa line shaft l5 driven periodically insynchronism with the opening andclosing of the chucks Hi. It will be understood that when the chucks IIIare open the carriages II are returned to the beginning of their feed-30 ing positions, the chucks are then closed about the casing so thatthe forward feeding movement of the carriages ll moves the casing anincrement into the press. This forward feeding movement of the casingoccurs when the die mam-- 35 bers of the press are open and isaccompanied .by rotation of the casing about its axis. In the apparatusillustrated the casing is turned about its axis by gearing l6 connectedto the shafts l4 and serving to rotate the chucks H].

In Fig. 11, die I9 is illustrated as being formed of three complementalmembers or parts which are alike in extent, interior configuration andgeneral shape. Each member is provided interiorly with a groove soshaped that when the members are in closed die-forming position theinterior of the die is provided at an end with an outwardly flaring bellsection for facilitating the entering and centering of a casing in thedie. Adjoining the bell section there is a truncated conical section 2|which converges inwardly from the entering end of the die and whichserves to plastically compress to tapered form successive increments ofa casing. The

axial length of this section is preferably several times the diameter ofa casing to be straightened. By way of example, and not of limitation,its length may be about three feet for the straightening of easing eightinches in diameter. The difference between the large and smalldiameterends of tapered section 2| depends upon the extent it may be desired toreduce the diameter of casing beyond that required for straightening it.In the straightening of casing of plain steel having a carbon content ofabout .35 per cent to .50 per cent, it is sufficient to re duce itsdiameter not more than about two per cent. Any additional reduction indiameter serves to increase the hardness and yield point of the metalbeyond that ordinarily obtained in straightening the casing according tomy invention. v

Immediately adjoining the small-diameter end -of the truncated conicalsection 2| of the die, there is a cylindrical section 22 in axialalignment with the conical section having a diameter that is preferablythe same as that of the inner end of the truncated conical section. Thelength of the cylindrical section is preferably about the same as thatof the truncated conical section, or, in other words, several times thediameter of the casing to be straightened. Specifically, the length ofthe cylindrical section of the die depends upon the stepped forward feed.of the casing rather than on the diameter of the casing. Preferably thecylindrical section is of the same length in dies of different sizecapable of operating on casings of various diameters except that in thebigger casing sizes having heavier walls a shorter cylindrical lengthmay be used. The length of the tapered section of the die depends uponthe number of reductions required to get uniform cold workcircumferentially of the casing assuming a given axial and rotary feedof the casing. Each of the cylindrical and tapered sections of the dieshould be longer than one diameter of the casing.

In Figs. 4 to 10, inclusive, there is illustrated a series of successivesteps performed by the lateral reciprocation of the die members and therotation and advancement of the casing in the straightening of a wellcasing C according to the preferred practice of my invention and by theuse of the particular die herein disclosed. For simplicity, thesuccessive stages are illustrated in connection with only one of the diemembers. In Fig. 4 the die is shown in its open casing-receivingposition, and the casing is shown as having its first or forward endincrement a moved into the die. This and the suceceeding increments maybe about one-half the length of the tapered section 2| of the die, asillustrated, although it will be understood that the length of theincrements may vary with relation to the length of this section of thedie. When the die is closed by inward reciprocation radially of thecasing, the first increment a is plastically compressed to tapered form,as shown in Fig. 5. Thereafter, the die is opened, and, during the timethat it is not in engagement with it, the casing is moved longitudinallyto enter its second increment b, and it is also turned or rotated on itsaxis an angular amount substantially equal to one-half the a'rcuateextent of the groove of each die member, or, in other words, it isrotated about 60 when three-part dies such as illustrated are used.

In the second closing ,movement of the die, increment a is furtherplastically reduced, and increment b is plastically reduced the same aswas increment a in the stage of the operation illustrated in Fig. 5. Inthe next stage, shown in Fig. 8, the die is opened and the casing isrotated on its axis and advanced longitudinally to present its nextincrement c .to the die in the manner explained above. In this stage ofthe operation increment a lies in the forward end of the cylindricalsection 22 of the die. The diameter of this section is sufllciently lessthan the small-diameter end of increment a that upon the closing of thedie the metal of the casing forming this increment is plasticallycompressed and molded to cylindrical form in the manner illustrated inFig. 9, which also shows increments b and c as being reduced and moldedto progressively smaller tapered form. When -the die is'opened after themolding of increment a to cylindrical form, the elasticity of the metalincreases the diameter of this increment somewhat beyond that of thecylindrical portion of the die. In the next stage of the operation,illustrated in Fig. 10, increment a is elastically compressed, withoutany permanent reduction in its diameter, to the diameter of increment bwhich is then being plastically compressed to cylindrical form. Thestages of the operation that have been described with reference to Figs.5 to 10 are repeated until the entire casing has passed through thestraightener, the casing being advanced increment by increment andturned on its axis between each diameter-reducing and molding operationof the die.

It will be observed that in the cold-straightening of well casingaccording to my invention, the casing is progressively reduced indiameter an amount suillcient to cause a substantial plastic flow of allits metal, and that while the metal is subjected to such flow it ispositively molded to desired cylindrical form in increments of suchlength that they retain their molded form. Furthermore, each incrementis molded to its cylindrical form in positive axial alignment with anadjoining elastically compressed increment that has previously beenmolded to the same cylindrical form. Thus the entire casing is not onlystraightened, but is made cylindrical. By turning the casing on its axisbetween its incremental and progressive reduction in diameter, thepressure is so applied to the metal as to cause itsplastic flow to besubstantially uniform around the body of the casing and from end to end.As a. result of this, the cold-straightened casing is free ofobjectionable residual stresses.

The practice of my invention not only straightens the casing but alsosizes it in a single simultaneous operation. Heretofore casingordinarily has been sized in a sizing mill while still hot, and unlessthe temperature of the casing is within close limits during sizing it isunder or over size According to the provisions of the patent statutes, Ihave explained the principle and mode of operation of my invention, andhave illustrated and described what I now consider to be the best way ofpracticing it. However, I desire to have it understood that, within thescope of the appended claims, my invention may be practiced otherwisethan as specifically illustrated and described.

I claim as my invention:

1. The method of cold-straightening well casing formed of steel,comprising reducing it in diameter substantially without elongation bysubjecting it increment after increment and progressively from'end toend to repeated radial pressure applied solely to the exterior of thecasing and substantially uniformly around its circum- Ierence, and whilethus subjected to plastic flow concurrently molding the increments toaxially aligned uniform-diameter cylindrical form.

2. The method of cold-straightening well casing formed of steel,comprising reducing it in diameter without substantiallyany elongationby subjecting it increment after increment and progressively from end toend to repeated radial pressure applied solely to the exterior of theeasing and substantially uniformly around its circumference, and whilethus subjected to plastic flow concurrently molding the increments firstto tapered form and then to axially aligned uniformdiameter cylindricalform.

3. The method of cold-straightening well casing formed of steel,comprising reducing it in diameter without substantial elongation bysubjecting it increment after increment and progressively from end toend to repeated radial pressure applied solely to the exterior of thecasing and substantially uniformly around its circumference, and whilethus subjected to plastic flow concurrently molding the increments toaxially aligned uniform-diameter cylindrical form, and turning thecasing on its axis between the applications of said diameter-reducingand molding pressure.

4. The method of cold-straightening well casing formed of steel,comprising reducing it in diameter but substantially without elongationby subjecting it increment after increment and progressively from end toend to repeated radial pressure applied solely to the exterior of thecasing and substantially uniformly around its circumference,concurrently molding the increments first to tapered form and then toaxially aligned uniform-diameter cylindrical form, and turning thecasing on its axis between said applications of diameter-reducing andmolding pressure.

5. The method of cold-straightening well casing formed of steel,comprising reducing it in diameter without substantially any elongationby subjecting it increment after increment and progressively from end toend to repeated radial pressure applied solely to the exterior of thecasing and substantially uniformly around its circumstance, and whilethus subjected to plastic flow concurrently molding the increments toaxially aligned uniform-diameter cylindrical form, and maintainingcylindrically molded increments in axial alignment with those beingmolded.

6. The method of cold-straightening well casing formed of steel,comprising reducing it in diameter without substantially any elongationby subjecting it increment after increment and progressively from end toend to repeated radial pressure applied solely to the exterior of theeasing and substantially uniformly around its circumference,concurrently molding the increments first to tapered form and then toaxially aligned uniform-diameter cylindrical form, turning the casing onits axis between said applications of diameter-reducing and moldingpressure, and maintaining cylindrically molded increments in axialalignment with those being molded.

7. The method of straightening well casing from end to end and withoutsubstantially any elongation which comprises reducing the casing indiameter between dies increment after increment and progressively fromend to end and while unsupported internally, each increment being firstreduced in diameter in the entering part of the die and subsequentlyfurther reduced in diameter in other parts of the die while concurrently a succeeding increment is reduced in the entering part of thedie, the casing being advanced longitudinally and rotated axiallybetween each reduction, and while being reduced in diameter maintainingthe increments in alignment with that portion of the casing that hasbeen straightened.

8. The method of cold-straightening well casing which comprisesprogressively reducing the casing in diameter in a tapered multi-piecedie, advancing the casing axially into a smaller part of the tapered diebetween compressive movements thereof, rotating the casing about itsaxis approximately one-half the arcuate extent of a piece of the dieduring the advancing movement of the casing, further reducing the casingin diameter in a tapered part of the die, advancing the casing into acylindrical part of the die between compressive movements thereof whilerotating the casing about its axis so that the pass line of the dies isremote from the previous one with respect to the casing, furtherreducing the casing in diameter in the cylindrical part of the die,advancing the casing into the cylindrical part of the diebetweencompressive movements thereof while rotating the casing about itsaxis so that the pass line of the die is remote from the previous onewith respect to the casing, and

compressing the increment of the casing last reduced in the cylindricalpart of the die but within the elastic limit of the metalthereof so asto hold its axis in alignment with the axis of other increments beingsized and straightened.

9. That method of sizing and straightening an oil well casing whileavoiding and relieving stress concentrations therein which comprisesforming a taper on the end of the internally unsupported casing bypressure applied substantially simultaneously over the entirecircumference of the portion of the casing tapered so that the taper isvisible on the inner and outer surfaces of the casing, turning thecasing through a partial are about its longitudinal axis, again but in aseparate operation extending the taper over a greater length of thecasing by similarly applied pressure, then step by step moving the taperback from the end of the casing by plastically flowing and positioning aportion of the casing at the small end of the taper parallel with theaxis of the casing, said portion of the casing positioned parallel withthe axis being equal to the distance the taper is moved back on eachstep from the end of the easing and holding the parallel portion of thecasin so that its axis is in parallel relationship with the axis ofthose portions of the casing being formed.

10. The method of cold sizing and straightening oil well casing whichcomprises reshaping the entire wall of the end of the casing withoutinternal support and by plastic flow of the cold metal to formsubstantially atruncated hollow cone the base of which has a diameterequal to the ,original diameter of the casing, advancing and rotatingthe casing about its axis, extending the length of the cone by incliningmore of the wall of the casing by plastic flow of the metal and whilemaintaining the base diameter of the cone, thereafter advancing androtating the casing, again extending the length of the cone as lastdescribed and simultaneously by plastic flow positioning parallel withthe casing axis a length of the casing at the small end of the coneequal to the extension in length of the cone, and repeating theadvancing and rotation of the casing and the last-named cone extendingand wall positioning steps until the entire length of casing is formedwith a reduced diameter and aligned walls parallel to the casing axis.

11. That method of sizing and straightening oil well casing whichcomprises applying pressure relatively slowly over the outside only ofthe end of the casing to cause a plastic flow of the metal, controllingthe direction and extent of the plastic flow to form a substantiallyconical taper on the end of the casing both on the inside and outside ofthe casing and without any appreciable change in wall thickness orelongation of the casing, advancing and rotating the casing about itsaxis relative to the pressure-applying zone, repeating the applicationof pressure as before and while the metal at the small end of the taperis flowing plastically controlling the direction and extent of the flowto reposition the casing wall at the small end of the taper parallelwith the axis of the casing and to a uniform diameter.

